The present invention relates to a multilayer insulated wire having two or more insulating layers, and a transformer wherein the same is utilized. More specifically, the present invention relates to a multilayer insulated wire having excellent heat resistance and high-frequency properties and useful as a lead wire and a winding used in a transformer to be incorporated in electronic/electrical equipment and the like. The present invention also relates to a transformer that utilizes the multilayer insulated wire.
The structures of transformers are stipulated, for example, in IEC standards (International Electrotechnical Communication Standards), Pub. 950. These standards stipulate, for example, that, in the windings, the enamel film coating the conductor is not recognized as an insulating layer; an insulator having a stipulated thickness, or a thicker insulator, is to be inserted between the primary winding and the secondary winding; or, a three-layer insulator, wherein, out of the three layers, two arbitrary layers pass the test of the stipulated withstand voltage (in the case of an operating voltage of 1,000 V, they should withstand for 1 min or more with 3,000 V being applied), is to be inserted between the primary winding and the secondary winding; and a stipulated creeping distance is to be taken between the primary winding and the secondary winding.
Accordingly, in the currently predominant transformer, wherein an enameled wire is used, the structure shown in FIG. 2 in cross section, for example, is employed. That is, the structure is such that insulating barriers (2), for securing a creeping distance, are arranged on opposite ends of the circumferential surface of a bobbin (1); a primary winding (3) is wound between the insulating barriers; an insulating tape (4) is wound thereon at least three times; and then insulating barriers (2), for securing a creeping distance, are arranged on opposite ends of the circumferential surface, and a secondary winding (5) is wound between them.
Additionally, in recent years, in place of the transformer having the structure shown in FIG. 2, a transformer having the structure shown in FIG. 1 in cross section, for example, has begun to appear. The feature of this transformer hasan overal is that it is small zize ,by omitting the insulating barriers (2) and the insulating tape (4), by using an insulated wire having at least three insulating layers as the primary winding (3) and/or the secondary wire (5). In the example shown in FIG. 1, the primary winding (3) has three insulating layers (3b, 3c, and 3d) on the outer circumferential surface of a conductor (3a). This structure brings about an advantage that the number of steps of operations for winding the insulating barrier (2) and the insulating tape (4) can be reduced/omitted.
Known of such a three-layer insulated wire include are one in which a first insulating layer is formed by winding an insulating tape around the outer circumference of a conductor, and then another insulating tape is wound around thereon, to form a second insulating layer, and then a third insulating layer is formed thereon; and one in which, instead of the insulating tapes, a fluororesin is successively extruded onto the outer circumference of a conductor, to form three insulating layers in all (JU-A-3-56112(xe2x80x9cJU-Axe2x80x9d means unexamined published Japanese utility model application)).
However, the insulation by the above insulating tape winding cannot avoid the winding operation, and therefore it has the problem that the productivity is tremendously low, to increase the production cost. Further, although the above insulation with a fluororesin is excellent in heat resistance and high-frequency properties, the cost of the resin is high, and further, when the conductor is pulled at a high shear rate, the state of the external appearance characteristically deteriorates. Therefore it is difficult to increase the production speed, leading to the fault that the cost of the electric wire with the fluororesin is made very high, similar to the insulating tape winding, and the production cost of the transformer is increased as a result. To solve such problems, the inventors of the present invention proposed, for example, an insulated wire in which a polyester resin that is modified so that crystallization may be prevented from occurring and reduction of the molecular weight may be suppressed, is extruded onto the outer circumference of a conductor, to form a first and a second insulating layer, and then a polyamide resin is extruded as a third insulating layer for the covering (JP-A-6-22334 (xe2x80x9cJP-Axe2x80x9d means unexamined published Japanese patent application (U.S. Pat. No. -A-5,152)).
However, it cannot be said that such a multilayer extrusion-coating insulated wire satisfactorily meets the demand for improvement in the performance of transformers in the future, which will become more and more strict.
First, as electrical/electronic equipments have been made small-sized in recent years, the influence of heat generation on a transformer becomes remarkable therefore, even in the case of the above three-layer extrusion coating insulated wire, higher heat resistance is demanded. Further, the frequency used in circuits of transformers are into high frequencies, and therefore improvements in electrical properties at high frequencies are demanded.
To meet such demands, the inventors of the present invention proposed, as a multilayer insulated wire improved in heat resistance, an electric wire covered with an inner layer of a polyethersulfone and the outermost layer of a polyamide (JP-A-10-13442).
An object of the present invention is to provide a multilayer insulated wire that solves the above problems involved in conventional multilayer insulated wires, that realizes such high heat resistance as heat resistance F class (155xc2x0 C.), which satisfies IEC 950 standards, or;
higher heat resistance, in transformers; and that can exhibit excellent electrical properties even at high frequencies.
Further, another object of the present invention is to provide a transformer wherein, when it is used at high frequencies, the electric properties are not lowered, and influence by the generation of heat is prevented.
Other and further objects, features, and advantages of the invention will appear more fully from the following description, taken in connection with the accompanying drawings.
In view of the above objects, the inventors of the present invention, having investigated intensively, have found that, when at least one layer out of two or more extrusion-coating insulating layers is formed by using a mixture of 100 parts by weight of a polyethersulfone resin as a favorably extrudable heat-resistant resin with 10 to 100 parts by weight of an inorganic filler, the heat resistance is further improved, the electric properties at high frequencies are improved, and , further, the heat shock resistance (crack prevention) and the solvent resistance of the coating insulating layer are improved. The present invention is completed based on the above findings.
That is, according to the present invention there is provided:
(1) A multilayer insulated wire having two or more extrusion-coating insulating layers provided on a conductor directly or via some other layer, or provided on the outside of a multicore wire composed of conductor cores or insulated cores that are collected together, wherein at least one of the insulating layers is made of a mixture prepared by mixing 100 parts by weight of a polyethersulfone resin and 10 to 100 parts by weight of an inorganic filler;
(2) A multilayer insulated wire having two or more extrusion-coating insulating layers provided on a conductor directly or via some other layer, or provided on the outside of a multicore wire composed of conductor cores or insulated cores that are collected together, wherein at least one of the insulating layers is made of a mixture prepared by mixing 100 parts by weight of a polyethersulfone resin and 20 to 70 parts by weight of an inorganic filler;
(3) The multilayer insulated wire as stated in the above (1) or (2), wherein the insulating layer made of the mixture is formed at least as the outermost layer.
(4) The multilayer insulated wire as stated in the above (1), (2), or (3), wherein the proportion of the inorganic filler in the mixture is increased in an outer layer than an inner layer, successively.
(5) The multilayer insulated wire as stated in any one of the above (1), (2), (3), or (4), wherein the inorganic filler comprises at least one selected from among titanium oxide and silica.
(6) The multilayer insulated wire as stated in any one of the above (1), (2), (3), (4), or (5), wherein the inorganic filler has an average particle diameter of 0.1 to 5 xcexcm.
(7) A multilayer insulated wire, comprising the multilayer insulated wire stated in any one of the above (1), (2), (3), (4), (5), or (6) whose surface is coated with a paraffin and/or a wax; and
(8) A transformer, wherein the multilayer insulated wire stated in any one of the above (1), (2), (3), (4), (5), (6), or (7) is utilized.
Meanwhile, the outermost layer in the present invention refers to the layer situated farthest from the conductor out of the extrusion-coating insulating layers.